1. Field of the Invention
The present invention relates to a liquid container, an ink jet cartridge and an ink jet printing apparatus.
2. Related Background Art
For ink jet printing apparatuses, a large number of means for supplying ink to an ink jet print head have been proposed and in practical use. The most traditional ink supply method for ink jet printing apparatuses is a tube supply method of supplying ink from an ink tank in the printing apparatus to a print head on a cartridge via a tube. However, according to such a tube supply method, the movement of the cartridge affects the flow of the ink in the tube in the direction in which the carriage moves, so that the ink may be ejected unstably from the print head. Thus, oscillation of the ink in the tube must be suppressed in order to increase printing speed.
Further, the tube supply method has various problems associated with the need for a tube long enough to allow the carriage to be reciprocated. For example, to avoid inconveniences attributed to the entry of air into the tube during a long-time storage, a large amount of ink from an ink supply source (an ink tank) must be allowed to flow through the tube when the printing apparatus is initially used or in other cases. Moreover, the above described tube is used as only a path through which ink from the ink tank is supplied to the print head. Thus, the tube does not only have a smaller added value but also results in an increase in the size and cost of the printing apparatus and a complication of the structure, or the like.
To omit such an ink supply tube, an ink jet printing apparatus of FIG. 15 has been developed which employs a so-called head-tank-on carriage method. The ink jet printing apparatus 100 shown in FIG. 15 comprises an ink jet cartridge 101 including an ink jet print head and an ink tank detachable from the print head. The ink jet cartridge 101 is installed onto a carriage 103 that can reciprocate in a main scanning direction while being guided by a guide shaft 102. The ink jet printing apparatus 100 alternately repeats an operation of ejecting ink from the print head in the ink jet cartridge 101 on the basis of print data and an operation of conveying a print medium P in a sub-scanning direction perpendicular to the main scanning direction.
The ink jet printing apparatus 100 includes a capping unit 104 that caps ink nozzles of the print head of the ink jet cartridge 101. A recovery process (preliminary ejection) for maintaining an appropriate ink ejection state can be executed by making the print head eject ink not contributing to image printing on the capping unit 104. Further, a suction recovery process for maintaining an appropriate ink ejection state can be executed by generating negative pressure in the capping unit 104, which caps the ink nozzles of the print head, to forcibly suck ink from the ink nozzles of the print head. The print head of the ink jet cartridge 101 includes, for example, electrothermal converting elements in order to eject ink droplets through the ink nozzles. In this case, the electrothermal converting elements generate heat to subject the ink to film boiling. The print head ejects ink droplets through the ink nozzles using thermal energy generated by the electrothermal converting elements.
In the head-tank-on carriage method, the ink supply path is formed between the print head and ink tank of the ink jet cartridge 101. This enables the configuration of the ink supply path to be significantly simplified. Further, the ink supply path is integrally incorporated in the print head or the ink tank, so that the size and costs of the apparatus can be reduced and a shorter ink supply path can be designed. It is also possible to drastically reduce a portion of the ink supply path extending in parallel with the movement direction of the carriage 104. This effectively suppresses unstable ink ejection attributed to the oscillation of ink in the ink supply path during high-speed printing.
However, in the head-tank-on carriage method, if a large amount of ink is stored in the carriage, the capacity of the ink tank constituting the ink jet cartridge must necessarily be increased. An increase in the size and/or weight of the ink jet cartridge increases the weight of the entire carriage, on which the ink jet cartridge is installed. This may increase the size of a motor that drives the carriage, driving power, and the size and weight of the entire printing apparatus. On the other hand, for small-sized ink jet printing apparatuses, it is desirable to minimize the size of the carriage. Accordingly, the capacity of the ink tank installed on the carriage is limited to an extremely small value. In such a case, the user must frequently replace the ink tank on the carriage. However, the frequent replacement of the ink tank does not satisfy demands for user-friendly apparatuses and environment preservation.
Ink jet printing apparatuses employing a so-called pit-in method are known to be able to solve above described problems. In the ink jet printing apparatus using the pit-in system, an ink supply to the sub-tank is performed as follows. At first, the carriage is moved to a predetermined ink supply position, for example, an end of the movement passage of the carriage. At the ink supply position, the sub-tank is connected to a main tank if necessary and is connected to a pump. Then, a negative pressure is created in the sub-tank by the pump to draw ink from the main tank into the sub-tank by suction. Further, the sub-tank on the carriage is filled with ink from a main tank provided in the printing apparatus. With such a pit-in method, the weight of the entire carriage is reduced to enable the print head to carry out high-speed scanning. As a result, high-speed printing is achieved. Further, as long as the sub-tank is filled with ink from the main tank, the number of sheets printed is not limited. Furthermore, it is unnecessary to have such a tube as is required for the above described tube supply method. This simplifies the configuration of the entire apparatus.
The most important technical point of such a pit-in method is how to reliably fill the sub-tank with ink. That is, the most important point is how to supply ink from the main tank to the sub-tank during a pit-in operation at the home position.
An example of such an ink supply method used during a pit-in operation is a method of providing a sensor in the sub-tank to detect the amount of ink and supplying ink to the sub-tank in accordance with the detected amount of ink. However, a mechanism for this method is very complicated, delicate, and expensive. To solve this problem, a method is known including sucking all ink from the sub-tank during a pit-in operation and subsequently filling the sub-tank with ink. This method eliminates the need to add means for detecting the amount of ink in the sub-tank. However, the total amount of waste ink sucked from the sub-tank during each pit-in operation is not negligible. Thus, it is necessary to increase the size of area in which the waste ink is stored. Also, tight design restrictions are imposed on, in particular, small-sized ink jet printing apparatuses.
To solve these problems, a pit-in-method-based ink supply means has been proposed which employs a gas liquid separation member as shown in FIGS. 16 and 17. The example shown in these drawings blocks the flow of a liquid (ink), while utilizing the nature of the gas liquid separation member, which allows a gas such as air to pass through. In this case, before the carriage moves to the home position, a sub-tank unit 200 on the carriage is separated from an ink supply recovery unit 201 of a main tank disposed at a predetermined position of the printing apparatus, as shown in FIG. 16. In the state shown in FIG. 16, the level L of ink in a container main body 206 is low.
An ink absorbing member 224 is accommodated in the container main body 206 of the sub-tank unit 200. Ink in the container main body 206 is supplied to the ink jet print head 226 through a filter 225. A suction path is formed in the upper part of the container main body 206 and is in communication with a suction port 227 via a gas liquid separation member 223. Further, the sub-tank unit 200 has a hollow needle 222 that is in communication with the suction port 227. On the other hand, the ink supply recovery unit 201 has a suction joint 229 that can be connected to the suction port 227 of the unit 200 and is connected to a suction pump (not shown). Further, a supply joint 230 is disposed close to the suction joint 229 and can be connected to the hollow needle 222 of the unit 200. The supply joint 230 is connected to the main tank (not shown) via an ink supply path. An air communication passage opened and closed by a valve body 228 and a suction path connected to the suction pump are connected to a cap 208 that can cap the print head 226.
During a pit-in operation, the units 200 and 201 are moved closer to each other and then coupled together as shown in FIG. 17. Then, ink from the unit 201 in the main tank is supplied to the unit 200 in the sub-tank. That is, as shown by the solid arrow in FIG. 17, the suction pump sucks air from the container main body 206 of the unit 200 through the suction joint 229, the suction port 227, and the gas liquid separation member 223. As a result, negative pressure is generated in the container main body 206. Accordingly, as shown by the dotted arrow in FIG. 17, ink from the main tank is introduced into the container main body 206 through the supply joint 230 and the hollow needle 222. Once the level L of ink in the container main body 206 rises to the level of the gas liquid separation member 223, the gas liquid separation member 223 starts to block the passage of ink. Consequently, the ink supply is automatically stopped.
The amount of air sucked by the suction pump has only to be at least the internal volume of the container. By sucking air from the container main body 206, the air is discharged from the container main body 206 through the gas liquid separation member 223 regardless of the amount of ink remaining in the container main body 206. Instead, ink from the main tank is supplied into the container main body 206. That is, to fill the container main body 206 with ink, a specified or larger amount of air has only to be sucked from the container main body 206 through the gas liquid separation member 223. Thus, it is unnecessary to control the sucking of air. In principle, the inside of the container main body 206 can be filled with ink by designing the suction pump with a sufficient margin.
Recently, ink jet printing apparatuses have accomplished remarkable advances. It is also common to implement high-definition color images having photograph quality. Further, with the expansion of the markets, there are growing demands for more inexpensive printing apparatuses with higher quality. Naturally, such demands also exist for small-sized and pit-in-method-based printing apparatuses previously described. Such demands for colored and more inexpensive printing apparatuses pose various problems in actually applying a configuration as shown in FIGS. 16 and 17.
That is, if the configuration of FIGS. 16 and 17 is applied to a pit-in-method-based printing apparatus capable of color printing, sub-tanks (ink containers) for a plurality of colors and pit-in structures for the respective colors must be provided to allow the multiple colors to be simultaneously printed. Further, in this case, if providing relatively expensive gas liquid separation member for each of the ink absorbing members, the number of sub-tank unit components and the number of assembly steps increase. Thus, it is difficult to reduce the costs of the printing apparatus. Further, when the gas is sucked from the ink absorbing members via the gas liquid separation members, ink is likely to be attached to the gas liquid separation members. In this case, if the ink remains on the gas liquid separation members, the characteristic (suction characteristic) of ventilation through the gas liquid separation members is deteriorated. Thus, it is difficult to stabilize the supply of ink to the ink absorbing members in the sub-tanks and maintain reliability.
To solve the above described problem associated with the number of gas liquid separation members, it is contemplated that a single common gas liquid separation member may be provided for each of the ink absorbing members. However, even this configuration fails to solve the problem that ink remains on the gas liquid separation members as described above. Alternatively, to prevent ink from remaining on the gas liquid separation members, it is contemplated that the shape of the ink absorbing members is modified so that ink easily returns from the gas liquid separation members to the ink absorbing members. However, in this case, the shape of the ink absorbing members becomes complicated, thus increasing the costs of the sub-tank unit and thus the entire printing apparatus. Furthermore, the gas liquid separation members may interfere with the ink absorbing members and vice versa. This may cause the leakage of ink or internal air.